Flare stack

ABSTRACT

Flare stack smoke is reduced or eliminated by controlling the temperature of the flare. Said temperature is sensed by a sensing element e.g. one or more thermocouples connected in parallel and located in the vicinity of the flare; the sensing element produces a signal which directly or indirectly activates steam control valve to adjust the flow of steam to the tip of the flare stack so as to raise or lower the flare temperature to the temperature of optimum combustion of flare stack effluent.

United States Patent Jasinsky et al.

[ FLARE STACK [72] inventors: Victor Jasinsky; Ambrose T. Upfold, bothof Sarnia, Ontario, Canada [73] Assignee: Polymer Corporation Limited[22] Filed: Aug. 4, 1970 [2l Appl. No.: 60,831

[52] U.S.Cl ..1l0/1l9, 431/202 [51] Int. Cl ..F23j 15/00 [58] FieldofSearch ..l10/1l9; 431/202 [56] References Cited UNITED STATES PATENTS3,456,606 7/1969 Withorn ..1 10/1 19 June 6, 1972 ..llO/ll9 5/1970Withorn 6/ 1959 Webster et al Primary Examiner-Edward G. FavorsAttorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT Flare stack smokeis reduced or eliminated by controlling the temperature of the flare.Said temperature is sensed by a sensing element e.g. one or morethermocouples connected in parallel and located in the vicinity of theflare; the sensing element produces a signal which directly orindirectly activates steam control valve to adjust the flow of steam tothe tip of the flare stack so a to raise or lower the flare temperatureto the temperature of optimum combustion of flare stack efiluent.

7 Claims, 2 Drawing Figures FATENTEDJUH 6 m2 I N V EN TOR S VICTORJASINSKY AMBROSE T. UPFOLD FLARE STACK This invention relates to a flarestack and in particular-to the smokeless combustion of flare stackgases.

Many industries and particularly petrochemical industry rely oncombustion to decompose by flame objectionable gaseous efiluents. Sucheffluents are piped to flare stacks of suitable height where they aremixed with steam and/or air and burnt. The feed rate of efiluents variesdepending on many factors and as a result the flare varies in size.Occasionally, during upsets in the operation, large amounts ofcombustible gases are directed to flare stacks to be burned causing theflare to increase. As the flare increases, its temperature rises andlarge amounts of black smoke are produced. To control smoke, steam isintroduced at the tip of the stack; it reduces the flare temperature andfacilitates complete combustion of gases. At the present time, thesupply of steam is manually controlled. Under normal conditions, thesteam usage is too high and inefficient. In the time of upsetoperations, however, it is used in inadequate amounts and the combustionof effluents is incomplete.

It is an object of this invention to provide an apparatus for automaticcontrol of the combustion in the flare. A further object is to provide aprocess for controlling flare stack smoke. And yet another object is toreduce air pollution caused by flare stack operation.

This invention provides an apparatus for controlling flare stack smokewhich comprises (1) a steam line leading to the flare, (2) a flowcontrol means in said line, (3) a sensing element in the vicinity of theflare, capable of producing a signal proportional to the temperature ofsaid flare, and (4) a transducer between said flow control means andsaid sensing element, said transducer being capable of converting thesignal to a force acting on said flow control means. The process ofcontrolling flare stack smoke in accordance with the invention comprisesthe steps of (a) sensing the temperature of the flare, (b) producing asignal, said signal being proportional to said temperature, and (c)adjusting steam flow to flare stack, the adjustment being proportionalto said signal, whereby the flare temperature is caused to correspond tothe predetermined temperature and the combustion of flare stack effluentis improved. v

The invention will be more fully described with reference to theattached drawings in which FIG. 1 is a side view of the upper part offlare stack and FIG. 2 is a schematic view of the control apparatus.

Referring to FIG. 1, reference numeral denotes a flare stack ending witha tip 11. The tip 1 1 is provided with an outlet of a steam line,usually in the form of multiple steam nozzles, and pilot light, neitherof which is shown in FIG. 1. A short distance below the tip 11 there isa platform 12. At the periphery of the platform there are located fourthermocouples 13, all of them in unobstructed view of, and preferablyequidistant from the tip 1 l. The distance between thermocouples and thetip is shown in FIG. 1 to be 7 feet, but it may vary from O to about 25feet.

The flare stack, usually a metal tubular structure, carries gaseousefiluent of egg. petrochemical plant to the stack tip, high above theground level, where they are mixed with air and steam and burnt. Theheight of the stack should be sufficiently high to protect surroundingprocess equipment from the heat of combustion, and to properly dispersethe products of combustion in the atmosphere.

The number of thermocouples in accordance with this invention may vary.If one thermocouple was used, the temperature measurement would not beconsistent; depending on wind conditions, the thermocouple would measureeither the temperature of the flare which would be very high or thetemperature of the atmospheric air. The measurement would be better ifthe thermocouple was attached to a vane and moved with the wind so as tobe always in the flare. Two thermocouples in diametrically oppositepositions at the tip would be better. In the absence of wind, they wouldmeasure approximately a temperature which would not be as high as thatat the center of the flare, but nevertheless indicative of the flaretemperature. In the case of wind blowing parallel to the line formed bythe two thermocouples, one thermocouple would record a low temperatureof ambient atmosphere and the second thermocouple would be close to thecenter of the wind-diverted flare and would record a high temperature.The average of two temperatures would be indicative of the flaretemperature. In the case of a wind blowing perpendicular to the lineformed by the two thermocouples, both thennocouples would record a lowtemperature of the oncoming wind and that temperature would not be trulyindicative of the flare temperature.

In accordance with this invention, it is preferred to have three or morethermocouples located around the flare so that an average temperatureindicative of the flare temperature is measured irrespectively andindependently of wind conditions. At least one of the thermocoupleswould be in the line of the wind-diverted flare and would record a hightemperature which would be then averaged with the temperature of theother thermocouples to produce an electric signal proportional to theaverage temperature, said average being indicative of the flaretemperature and indirectly of the flare size.

Any conventional thermocouple can be used provided it will stand themaximum temperature to which it may be exposed. If the thermocouple isto be located in the flare, above the tip of the stack, then a sheathedchromel-alumel thermocouple may be used. It is preferred to locatethermocouples some distance from the flare where the temperature will beconsiderably lower than in the flare but sufficiently high above theambient temperature; in such case, iron-constantan thermocouple is quitesatisfactory.

FIG. 2 shows schematically how the thermocouples are connected toproduce a signal which actuates corrective action on the valve so as toadjust the steam flow to a predetermined 0ptimum value. The four flarestack thermocouples 13 are connected in parallel with all the positiveleads connected to a conductor 14 and the negative leads to anotherconductor 15. The conductors are connected to a transducer: the positiveconductor is connected indirectly through an additional thermocouple 16measuring ambient temperature and connected in series so as tocounteract the effect of the flare stack thermocouples. The transducer17 produces a pneumatic signal which is fed through line 18 to anindicator and/or controller 19 provided with automatic and proportionaladjustments. The controller 19 is connected via line 20 to the controlvalve 21 on steam line 22 leading to the stack tip 1 1.

Each flare stack thermocouple produces a signal, an electromotive forcewhich is proportional to the temperature to which it is exposed. Theelectromotive force of each thermocouple is averaged as a result oftheir parallel arrangement and the average electromotive force which isproportional to the average temperature of all flare stack thermocouplesis transmitted to the terminals of the transducer. In locations wherethe seasonal temperature fluctuates widely and where the temperaturesensed by the flare stack sensing elements is significantly affected bythe ambient temperature, it is desirable to compensate for thatdisturbing variable. For that purpose, an additional thermocouple isconnected to the system as hereinabove described. The additionalthermocouple measures ambient temperature and produces an electromotiveforce which counteracts the average electromotive force produced by allflare stack thermocouples. Thus, the resulting electromotive force ofthe above circuit is independent of seasonal or day variations oftemperature; it is proportional only to the heat of combustion asmanifested in the flare temperature and indirectly to the flow rate ofeffluents to the flare stack.

The electromotive force fed to the transducer is converted to apneumatic signal such as an air or nitrogen pressure which is thentransmitted to recorder/controller 19. When the flow of eflluent isincreased, the flare temperature as detected by the flare stackthermocouples is also increased. This produces an error signal in thecontroller as the output pressure from the transducer moves away fromthe set point. The error signal bustion of effluent is complete withoutexcessive usage of steam.

The above described system was tested on a flare stack fired by gaseousC C hydrocarbon mixture. Smoke was practically eliminated and steamconsumption was reduced by about percent compared with the previouslyconventional manner ,of operation.

As has been said before, the described system is applicable to flarestacks fired by obnoxious fumes, vapors and/or gaseous effluents such asare used in various industries. Various modifications of the system andprocess are possible with respect to the number and location ofthermocouples or other sensing elements such as resistance temperaturedetectors, use of a compensating thermocouple, types of transducers andcontrolling elements without departing from the invention hereindescribed.

What is claimed is:

1. An apparatus for controlling flare stack smoke which comprises:

1. a steam line leading to the flare,

2. a flow control means in said line,

3. a sensing element in the vicinity of the flare, said elementconsisting of at least three thermocouples and being capable ofproducing a signal proportional to the temperature of said flare, and

4. a transducer between flow control means (2) and sensing element (3),said transducer being capable of converting said signal to a forceacting upon said flow control means.

2. The apparatus according to claim 1 in which the thermocouples areuniformly distributed around the flare.

3. The apparatus according to claim 2 in which the thermocouples aresubstantially equidistant from the flare at a distance of 0 to 25 feet.

4. The apparatus according to claim 1 in which all thermocouples areconnected so as to produce a single electrical signal.

5. The apparatus according to claim 4 in which there is an additionalthermocouple capable of producing a signal proportional to ambienttemperature and counteracting the single signal from the flarethermocouples.

6. A process of controlling flare stack smoke which comprises:

a. sensing and averaging the radiant heat in at least three directionsequidistantly from the flare, said heat being proportional to thetemperature of the flare,

b. producing a signal, said signal being proportional to the averagedradiant heat, and c. adjusting steam flow to the flare stack, theadjustment being proportional to said signal, whereby the averagedradiant heat is caused to correspond to the predetermined value and thecombustion of flare stack effluent is improved.

7. The process according to claim 6 in which the signal is an electricsignal corrected for the effect of variable ambient temperature.

1. An apparatus for controlling flare stack smoke which comprises:
 1. asteam line leading to the flare,
 2. a flow control means in said line,3. a sensing element in the vicinity of the flare, said elementconsisting of at least three thermocouples and being capable ofproducing a signal proportional to the temperature of said flare, and 4.a transducer between flow control means (2) and sensing element (3),said transducer being capable of converting said signal to a forceacting upon said flow control means.
 2. a flow control means in saidline,
 2. The apparatus according to claim 1 in which the thermocouplesare uniformly distributed around the flare.
 3. The apparatus accordingto claim 2 in which the thermocouples are substantially equidistant fromthe flare at a distance of 0 to 25 feet.
 3. a sensing element in thevicinity of the flare, said element consisting of at least threethermocouples and being capable of producing a signal proportional tothe temperature of said flare, and
 4. a transducer between flow controlmeans (2) and sensing element (3), said transducer being capable ofconverting said signal to a force acting upon said flow control means.4. The apparatus according to claim 1 in which all thermocouples areconnected so as to produce a single electrical signal.
 5. The apparatusaccording to claim 4 in which there is an additional thermocouplecapable of producing a signAl proportional to ambient temperature andcounteracting the single signal from the flare thermocouples.
 6. Aprocess of controlling flare stack smoke which comprises: a. sensing andaveraging the radiant heat in at least three directions equidistantlyfrom the flare, said heat being proportional to the temperature of theflare, b. producing a signal, said signal being proportional to theaveraged radiant heat, and c. adjusting steam flow to the flare stack,the adjustment being proportional to said signal, whereby the averagedradiant heat is caused to correspond to the predetermined value and thecombustion of flare stack effluent is improved.
 7. The process accordingto claim 6 in which the signal is an electric signal corrected for theeffect of variable ambient temperature.